1. Field of the Invention
The present invention relates to a document reading device such as a scanner which reads a document placed on a contact glass and converts it into digital data to be outputted to a computer, and more particularly, to the document reading device in which strange noises which a reading unit having a contact type image sensor (herein referred to simply as a CIS) may issue on contact with the contact glass, during scanning, can be effectively prevented.
2. Description of the Related Art
As publicly known, in the document reading device such as a scanner, a depth of focus is shallow. Therefore, reading by scanning is conducted in a state where a butting part of the CIS is kept in tight contact with a back face of the contact glass thereby to solve a problem of a focal length. However, because the butting part of the reading unit having the CIS frictionally slides on the back face of the contact glass, there will be generated such a drawback that a load may become large and strange noises may occur. Although a countermeasure of applying wax to the back face of the contact glass on which the butting part frictionally slides has been taken, the wax has been exhausted during the use, and it has been difficult for a user to recharge the wax, and hence, a long term use of the device has been unbearable. Besides, a wax applying work has been necessary in a production process.
In view of the above described problems, there has been a conventional document reading device including a reading unit which conducts scanning in contact with a contact glass thereby to read an image of a document placed on an opposite side through the contact glass, wherein the aforesaid reading unit is rotatably provided, and the reading unit is so adapted as to move in contact with the contact glass when the reading unit is moved in a direction of reading by scanning, and as to move apart from the contact glass when the reading unit is moved in an opposite direction to the direction of reading by scanning (See JP-A-2000-115474, for example).
However, in a structure disclosed in the above described JP-A-2000-115474 too, in order to read the image of the document, the reading unit is moved in tight contact with the contact glass, and so, there is a problem that the above described drawback cannot be essentially eliminated, though partially decreased.